In an LTE-A (long-term evolution-advanced) CA (carrier aggregation) system, multiple carriers are aggregated, and may communicate with a single terminal (UE, user equipment, also referred to as terminal equipment, and a terminal in brief) at the same time, that is, one terminal has multiple serving cells. In the multiple serving cells, one is a PCell (primary cell), and others are SCells (secondary cells). In an existing CA system, aggregated cells are all under coverage of the same base station (eNB), and belong to a CA system of the same eNB.
In the existing CA system, the eNB needs to configure terminal with measurement configuration, including:
measurement objects: the object on which the terminal shall perform measurements; for intra-frequency or inter-channel measurements of an E-UTRA (evolved universal terrestrial radio access) system, a measurement object is a single E-UTRA carrier frequency, and an E-UTRAN (evolved universal terrestrial radio access network) is able to configure a list of cell specific offsets and a list of “blacklist” cells associated with the carrier frequency, blacklisted cells being not considered in event evaluation or measurement reporting; for inter-RAT (radio access technology) UTRA (universal terrestrial radio access) measurement, a measurement object is a set of cells on a single UTRA carrier frequency; for inter-RAT GERAN (GSM (global system for mobile communication) EDGE (enhanced data rate for GSM evolution) radio access network) measurement, a measurement object is a set of GERAN carrier frequencies; and for inter-RAT CDMA2000 (code division multiple access) measurement of inter-RAT, a measurement object is a set of cells on a single HRPD (CDMA2000 high rate packet data) or 1×RTT (CDMA2000 1× radio transmission technology) carrier frequency;
reporting configurations: a list of reporting configurations where each reporting configuration consists of a reporting criterion and a reporting format, the reporting criterion being a criterion that triggers the terminal to send a measurement report, and may be periodical or a single event description, and the reporting format referring to the quantities that the terminal includes in the measurement report and associated information, such as the number of cells to report, etc.;
measurement identities: a list of measurement identities where each measurement identity links one measurement object with one reporting configuration; by configuring multiple measurement identities, it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object; and the measurement identity is used as a reference number in the measurement report;
quantity configurations: one quantity configuration is configured per RAT type, the quantity configuration defining the measurement quantities and associated filtering used for all event evaluation and related reporting of that measurement type, one filter can be configured per measurement quantity; and
measurement gaps: periods that the terminal may use to perform measurements, that is, no uplink (UL) and downlink (DL) transmissions are scheduled.
An E-UTRAN configures only one measurement object for a given frequency, that is, it is impossible to configure two or more measurement objects for the same frequency with different associated parameters, such as different offsets and/or blacklists. The E-UTRAN may configure multiple instances of the same event, such as configuring two reporting configurations with different thresholds.
Furthermore, a measurement event in the reporting criterion related only to the current system and used for triggering a measurement report further includes following six events:
event A1: a serving cell becomes better than a threshold;
event A2: a serving cell becomes worse than a threshold;
event A3: a neighboring cell becomes offset better than a PCell; wherein, a frequency used by the neighboring cell may be different from a frequency used by the PCell, and the neighboring cell may be a serving cell;
event A4: the neighboring cell becomes better than a threshold;
event A5: the PCell becomes worse than a threshold and the neighboring cell becomes better than another threshold; wherein, a frequency used by the neighboring cell may be different from a frequency used by the PCell, and the neighboring cell may be a serving cell; and
event A6: the neighboring cell becomes offset better than an SCell; wherein, the neighboring cell is at the same frequency as the SCell.
At a terminal side, in order to record the configuration and the procedure related to the measurements, two variables related to the measurement are stored, that is, a measurement configuration variable and a measurement report list variable.
Measurement configuration variable: the terminal stores in it accumulative configuration of measurement needing to be performed, the measurement including intra-frequency, inter-frequency and inter-RAT mobility related measurement. In this way, in each time of performing measurement configuration by an eNB on the terminal via air interface or executing a measurement-related procedure by the terminal, it is possible that the terminal may modify the measurement configuration variable stored by it. Particular contents of the measurement configuration variable include a measurement identity list, a measurement object list, a reporting configuration list, quantity configuration, an s-measure and a speed status parameter.
The measurement report list variable: the terminal stores in it related information on measurement satisfying a triggering condition, including a list of measurement having triggered report. Each measurement in the list triggering the report further includes a corresponding measurement identity, a list of cells in which report has been triggered, and the number of reports that have been transmitted.
In receiving the measurement configuration from the eNB, performing the measurement, reporting a measurement result and executing a measurement-related procedure, the terminal is possible to modify the measurement configuration variable and the measurement report list variable, such as a removal operation on a measurement identity performed by the terminal side. In the existing CA system, automatic removal of the measurement identity at the terminal side is only applicable to A1, A2 and A6 of the existing measurement events.
And on the other hand, in the existing LTE-A system, a macro cell is mainly deployed. As increase of an amount of traffics in the future, it is possible that small cells are further deployed. Coverage of a small cell is relatively small, but the number of the small cells is relatively large. Hence, if small cells are simply deployed only, and no control and structure optimization are performed, many problems, such as degradation of robustness of mobility, and increase of burden of control signaling, etc., will be resulted in. In order to solve these problems, and at the same time, in order to increase flows of single user, a new-type network protocol architecture, dual connectivity, is proposed in the industry. In the dual connectivity architecture, the terminal may communicate with multiple eNBs at the same time. For example, the terminal may communicate with a macro eNB and a small cell eNB at the same time, or may communicate with two small cell eNBs at the same time. In the eNBs communicating with the terminal at the same time, one eNB always provides the terminal with a control interface between the terminal and a core network, and this eNB is referred to as a primary eNB. Other eNBs than the primary eNB communicating with the terminal at the same time are referred to as secondary eNBs. And at the same time, in serving cells of the terminal, a cell group associated with the primary eNB is referred to as a primary cell group, and a cell group associated with the secondary eNBs is referred to as a secondary cell group.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.